1. Field of the Invention
The present invention relates in general to a frequency converter for reception of satellite broadcasting which is capable of receiving a satellite signal having polarized wave components with no use of a polarized wave converter, and more particularly to a frequency converter for reception of satellite broadcasting which is capable of receiving left and right circularly polarized waves of a satellite signal by phase-shifting vertically and horizontally polarized waves thereof.
2. Description of the Prior Art
FIG. 1A is a block diagram of a conventional frequency converter for reception of satellite broadcasting and FIG. 1B is a sectional view of a portion of a waveguide connected to a feed horn of a general satellite broadcasting receiver. As shown in these drawings, disposed at one side of a dielectric substrate 3 is a feed horn 4 through which incomes a satellite signal focused on an antenna (not shown) which is disposed in the front of the feed horn 4. The conventional frequency converter comprises a patch 1 which is disposed at the other side of the dielectric substrate 3, corresponding to the center of a diameter of the feed horn 4. Feeding lines 2 are disposed vertically to the center of the patch 1, respectively. The feeding lines 2 consist of vertical and horizontal feeding lines 2V and 2H disposed perpendicularly to each other. The vertical and horizontal feeding lines 2V and 2H are connected commonly to each other through first-stage low noise amplifiers Q1V and Q1H and a connection point thereof is connected to a second-stage low noise amplifier Q. The feeding lines 2 are inserted through a wall of a waveguide 5 into a space in which the patch 1 is formed, and arranged vertically to the center of the patch 1 and apart at a desired interval therefrom, respectively.
The operation of the conventional frequency converter with the above-mentioned construction will hereinafter be described.
The satellite signal with polarized wave components which is focused on the antenna and incomes through the feed horn 4 is transferred through a dielectric material of the dielectric substrate 3 to the patch 1 of conductor pattern, thereby causing the satellite signal to be electromagnetically formed at the conductor patch 1.
The satellite signal electromagnetically formed at the conductor patch 1 is electromagnetically coupled to the vertical and horizontal feeding lines 2V and 2H, so that a vertically polarized wave of the satellite signal and a horizontally polarized wave of the satellite signal are excited at the vertical and horizontal feeding lines 2V and 2H, respectively.
One of the vertically and horizontally polarized wave signals excited at the vertical and horizontal feeding lines 2V and 2H is selected by turning-on/off of the first-stage low noise amplifiers Q1V and Q1H and applied to the second-stage low noise amplifier Q, which amplifies the selected signal and outputs the amplified signal to a satellite broadcasting receiving circuit.
Herein, the first-stage low noise amplifiers Q1V and Q1H and the second-stage low noise amplifier Q may typically be transistors for low noise amplification. One of the vertically and horizontally polarized wave signals is selected according to whether a turning-on bias is applied to any one of the first-stage low noise amplifiers Q1V and Q1H.
That is, for reception of the vertically polarized wave signal, the first-stage low noise amplifier Q1V connected to the vertical feeding line 2V is turned on, while the first-stage low noise amplifier Q1H connected to the horizontal feeding line 2H is turned off. As a result, the vertically polarized wave signal excited at the vertical feeding line 2V is first-stage amplified by the first-stage low noise amplifier Q1V and then second-stage amplified by the second-stage low noise amplifier Q.
On the other hand, for reception of the horizontally polarized wave signal, the first-stage low noise amplifier Q1H connected to the horizontal feeding line 2H is turned on, while the first-stage low noise amplifier Q1V connected to the vertical feeding line 2V is turned off. As a result, the horizontally polarized wave signal excited at the horizontal feeding line 2H is first-stage amplified by the first-stage low noise amplifier Q1H and then second-stage amplified by the second-stage low noise amplifier Q.
However, the conventional frequency converter for reception of satellite broadcasting is desirable in that it can receive the vertically and horizontally polarized wave signals, but has a disadvantage of being incapable of receiving left and right circularly polarized waves of the satellite signal without a polarized wave converter for converting the left and right circularly polarized waves into the linearly polarized waves or the vertically and horizontally polarized waves. The polarized wave converter for converting the left and right circularly polarized waves into the linearly polarized waves is generally disposed in the feed horn and may typically be of a ferrite magnetic material or a dielectric slab. The polarized wave converter of the ferrite magnetic material is desirable in that it is convenient to use since it can electrically perform the selection for the left and right circularly polarized waves, but has a disadvantage in that it is high in price. Also, the polarized wave converter of the dielectric slab is desirable in that it is low in price, but has a disadvantage in that it is inconvenient to use since a position of the slab is manually altered. Moreover, since the reception of the linearly polarized waves is impossible in the reception of the left and right circularly polarized waves, the dielectric slab must be removed in the reception of the linearly polarized waves. This causes an additional inconvenience.